1. Field of the Invention
The present invention relates to a safeguard for a sanitary fitting for preventing the backflow of water into a feedline.
2. Discussion of the Background
Sanitary fittings are known, in which the quality of the feed water can be endangered upon re-suction of impure water into the feedline. These include, in particular, washbasin and sink fittings including pull-out hose shower bath tap units having a hose shower. It can occur in the case of fittings of this type that the shower is lying in a basin or in a bath when, for example, the feedline breaks. If the fitting is open at that moment, the water in the basin or the bath can be completely sucked out via the shower due to the negative pressure which is built up in the feedline due to the water flowing off. Fittings of this type must have safeguards, by means of which the re-suction of impure water into the feedline is prevented.
A safeguard of this type is known from German Offenlegungsschrift 3,805,462. This fitting has a shutoff valve which is connected in the flow path between the feedline and the outlet of the fitting. Branching off from the flow path, as seen in the flow direction of the water, after the shutoff valve is an aeration path, in which the two valves of the safeguard are connected. These valves are constructed as sensitive check valves which, under normal operating conditions, are in a closed position. Under conditions allowing backflow, the two valves open automatically and thus aerate the outlet and the feedline in order to prevent the backflow of the water. It is possible under normal operating conditions, in particular in the case of rapid closure of the shutoff valve, for a negative pressure to be built up briefly in the flow path following the shutoff valve, by which means valves of the safeguard can be caused to open, which can lead to the fact that a droplet can emerge through the valves. In order to prevent this, the German Offenlegungsschrift mentioned teaches that the two valves should be arranged successively in such a wa that the negative pressure in the case of a rapid interruption of the water-drawing process only affects the first valve situated nearer to the flow path. The result of the delay between the two valves is that, under these operating conditions, the second valve does not open, and thus a water droplet emerging through the first valve is caught in the region between the two valves. In the case of a negative pressure lasting longer, such as occurs under conditions allowing backflow, both valves of the safeguard open in order to aerate the outlet and to prevent backflow of water into the feedline. It is disadvantageous in this known safeguard that the two valves have to be coordinated with one another extremely precisely and that they cannot reliably prevent of the backflow of water into the feedline since they do not interrupt the flow path of the fitting for the water.
Furthermore, a so-called "combined safeguard" is known from DIN 1988, Part 4, which consists of a backflow preventer and a pipe aerator connected downstream from the latter as seen in the flow direction. Under conditions allowing backflow, the backflow preventer, constructed as a check valve, closes off the flow path, whereas the pipe aerator connects the outlet to the ambient air.